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That guy who argued rivet spacing with me at Oshkosh was dead wrong
He kept saying 4D spacing was fine for a stressed skin panel on a Cessna wing, and I proved it failed the edge distance test right there on his own project. Has anyone else had to shut down someone's bad advice in the middle of a crowded booth?
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troymorgan17h ago
4D spacing on a Cessna wing skin is actually pretty standard for a lot of field repairs I've seen out of Texas... that guy might have been using a different edge distance spec from a later revision of the Cessna manual though. I pulled up the 100-series structural repair manual once and it says 4D is fine for the main skin but not for the doubler plates around the spar caps. Maybe he was thinking of the secondary structure allowance where they let you slide on the spacing for non-critical stuff. The real issue is if the rivet line is inside the bend radius of the skin or if the hole is too close to the edge of that stiffener channel underneath... that's where the 5D rule actually kicks in. I've seen plenty of factory Cessna wings with 4D spacing that have held up for forty years in the salt air down here.
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